Arsenal have spent money this summer on Alexis Sanchez but without further signings, Arsene Wenger's squad must improve and step up from within if they're to challenge for the Premier League title. With that in mind, James McNicholas picks out five current players who must deliver.

Jack Wilshere
There is a huge onus on Jack Wilshere to make a positive impression in preseason. Even before his hedonistic holiday in Las Vegas was splashed all over the tabloids, this was set to be a huge summer for the midfielder. It's time for him to transform his potential into improved performances.

Last season, Wilshere faced criticism from many quarters. Paul Scholes, not one frequently prone to candid comments, wondered allowed whether or not Wilshere had even kicked on since his teens. An angry Wilshere tracked down Scholes' phone number to remonstrate with the former Manchester United midfielder. However, he must recognise that the best way to answer his critics is on the pitch. That starts with a strong preseason.

After his poolside misdemeanours, the pressure on Wilshere to deliver is greater than ever. His major injury problems appear to behind him. At 22, he is approaching an age where youth and inexperience are no longer an excuse. Wilshere must follow the example of Aaron Ramsey to recover from a spell of indifferent form and enhance his reputation.

Ignasi Miquel
There is a huge opportunity for the tall defender this preseason. If the Spanish youngster performs well in this summer's friendly matches, he could earn himself a surprise place in the senior squad for next season.

Arsenal are suffering from a desperate shortage of centre-backs. With Per Mertesacker not due back in training until mid-August and Thomas Vermaelen continually linked with a move to Manchester United, it's possible that the Gunners could start the season with Laurent Koscielny as their only senior centre-half.

Even if Arsenal sign a new central defender, they arguably need someone to fill a gap as fourth-choice. If Miquel impresses in this summer's Emirates Cup, that spot could yet be his.

Wojciech Szczesny
With Lukasz Fabianski having left for Swansea, Wojciech Szczesny will be bracing himself for a new challenge from the incoming No. 2. It looks for all the world as if that man will be Colombian David Ospina, who has said his goodbyes to his Nice teammates ahead of completing a move to Arsenal.

Although Fabianski enjoyed a good 2013-14 campaign, he was already damaged goods. A series of high-profile mistakes in the past ensured that he could never be a serious long-term rival to Szczesny. Ospina arrives with no such scars. He has a burgeoning reputation and enjoyed an impressive World Cup campaign.

Speaking in New York, Wenger admitted that he anticipates fierce competition for the No. 1 jersey: "You know at the start Szczensy will be the No. 1, then again we'll be down to performances and if Ospina shows that he is better, he will play."

The gauntlet has been laid down to Szczesny, and he will know he can not afford any sign of complacency if he wishes to retain his place.

Joel Campbell
Joel Campbell has boarded a plane to London to fight for what he calls his "Arsenal dream." Three summers ago, a protracted transfer saga ended with Campbell signing a deal with the Gunners. However, he's yet to represent them in an official game.

Joel Campbell is ready to make an impact at Arsenal.

In the past three seasons, he has played for three different clubs in three different countries. At 22, he is already a journeyman. Campbell doesn't want to be a footballing nomad anymore. He has the work permit he requires to play in the Premier League and wants to put down roots in London.

Much, of course, will depend on the impression he makes during preseason. Wenger will be watching the Costa Rican's contribution with a keen eye. After his eye-catching World Cup performances, Campbell's stock may never be higher. The Arsenal boss could yet be tempted to cash in on the forward while he still has the chance.

Mikel Arteta
Amid rumours of a new defensive midfielder coming in, Mikel Arteta is potentially playing to keep his place in the team. At the very least he's certainly playing to win a new contract. Arteta's current deal expires at the end of the coming season and he would like to sign an extension. However, he feels he deserves more than the one-year deal Wenger is reportedly prepared to offer.

Wenger is famously reluctant to offer long-term contracts to players over 30, and Arteta will turn 33 this season. Speaking in May, the Spanish midfielder argued: "Age can be an asset for the club. For me, a much bigger asset is someone who has played 125 games in three years compared to someone who has played 25, if he is 20 years old. That's my opinion."

Rhetoric can only do so much. Wenger is much more likely to make his decision based on what he sees on the pitch and the training field. Arteta must find new reserves of energy if he is to convince Wenger of his future at the club beyond 2014.

James McNicholas is a football writer and the man behind Arsenal blog Gunnerblog.com. You can follow him on Twitter @gunnerblog.